1. Field of the Invention
The present invention relates to a method of processing a linework which is photoelectrically read with an image reader, and more particularly, it relates to a method of erasing, thickening, or thinning borderlines such as ruled lines.
2. Description of the Prior Art
As is well known, there is such a conventional apparatus widely being made available, which electrically reads an original image containing a drawn linework with an image input device such as a monochromatic scanner, and then generates image data to fill the closed regions formed by the linework with designated colors. The image data thus obtained are used in a process work for printing and a computer graphic for providing designated colors to respective regions.
After completing the process of generating an image in which respective regions are filled with colors, these borderlines are no longer necessary and the same should be erased. A variety of prior arts have proposed methods of erasing borderlines. In these prior arts, regions R2 through R4 (FIG. 8) located on both sides of a borderline region R1, for example, are extended toward the region R1 so that these regions R2 through R4 come to contact with each other at the center of the region R1. The image thus obtained is satisfactory in visual impression thereof.
For example, as shown in FIG. 9, one of these prior arts employs a computer in order to trace the respective pixels on the circumferential line of the region R2, and then to extend the circumferential line up to the center of the borderline region R1. Then, the inner half of the triangle portion in the region R1 is replaced with the color of the extended portion of the region R2. The respective regions are subjected to the expansion and the color-replacement process, so that the respective borderlines are erased and the colors of the adjacent regions are given thereto. This prior art automated the manual operation, having been executed by process workers.
If an original image is too large or the same is represented at a high resolution, however, the number of the pixels included therein is large. In such a case, therefore, a very long time is needed for detecting closed loops and connection relationship between all the lineworks, and the processing cost also increases. For example, the above prior art is effective for processing small lineworks having a resolution of about 10 lines per millimeter and a maximum of several thousands of pixels in each direction on an image plane. Nethertheless, this prior art needs to spend a very long time when an object image includes a large linework having tens of thousands of pixels in each direction and tens of lines per millimeter in resolution, and thus, this prior art is not suitable for practical use.
There is another prior art in which a spatial filter having 3.times.3 components shown in FIG. 10, for example, is serially applied to the contact area of a borderline region and other regions. If the borderline region is located in the nine pixels PX1-PX9 of the spatial filter, the color of the corresponding region is replaced by the color of the adjacent region. Even when applying the prior art, it requires a long time for processing the linework having a high resolution and a large size.
As mentioned above, if the original image has a high resolution and too many pixels, any of those conventional arts needs to spend a very long time for processing the linework. This in turn results in the increased cost.
In particular, these problems become further serious as the resolution and the number of pixels included in lineworks are further increased in order to improve the reproduction accuracy and the image quality in an electronic process for printing.